The present invention relates to communication systems and more particularly to a two-way communication system.
Mobile two-way radio units (calling stations) are often equipped with tone calling devices. These devices are actuated prior to a message transmission in order to alert the base station (called station) operator of the incoming message. The tones may either be used to actuate a switch in the loudspeaker circuit of the base station and thus turn the speaker on in order to receive the incoming message for the base station operator or alternatively operate a buzzer or other signaling devices to alert the base station operator that a message is waiting for service.
The advantage of tone signaling is that the radio receiver of the base station is essentially shut off until an incoming message arrives for the operator at the base station and prevents extraneous noise from distracting the operator, including noise impulses that break squelch and calls for other base stations using the same frequency.
The problem that the mobile radio unit operator faces is that when he transmits a tone call to the base station, he has no way of knowing whether or not he has actually reached the base station.
While there are many manufacturers of tone calling equipment, there are no systems in use that provide a simple automatic acknowledgement or confirmation that the base station has received the calling tones.
This same problem also occurs in two-wire or four-wire communication systems, such as in a two-way line remote control system, computer control system and the like. When an operator in these line communication systems wishes to control a remote device or the operation of a computer, the operator at the control console has no way of knowing whether or not he has actually reached the device to be controlled or the computer to be operated.